94954580 automatic control of street light
TRANSCRIPT
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AUTOMATIC CONTROL OF STREET LIGHT
MAJOR PROJECT REPORT
SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE AWARD OF THE DEGREE
OF
BACHELOR OF TECHNOLOGY IN
ELECTRICAL ENGINEERING
Submitted by:
Malik Sameeullah Muneeb Ahmed Rizwanullah Ansari
(08EES31) (08EES50) (08EES62)
Under the supervision of
DR. TARIKUL ISLAM
ASSOCIATE PROFESSOR
DEPARTMENT OF ELECTRICAL ENGINEERING FACULTY OF ENGINEERING &TECHNOLOGY
JAMIA MILLIA ISLAMIA NEW DELHI-110025 INDIA
2012
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AUTOMATIC CONTROL OF STREET LIGHT
MAJOR PROJECT REPORT
SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE AWARD OF THE DEGREE
OF
BACHELOR OF TECHNOLOGY IN
ELECTRICAL ENGINEERING
Submitted by:
MALIK SAMEEULLAH (08-EES 31)
MUNEEB AHMED (08-EES 50)
RIZWANULLAH ANSARI (08-EES 62)
Under the supervision of
DR. TARIKUL ISLAM
ASSOCIATE PROFESSOR
DEPARTMENT OF ELECTRICAL ENGINEERING FACULTY OF ENGINEERING &TECHNOLOGY
JAMIA MILLIA ISLAMIA NEW DELHI-110025 INDIA
2012
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DEPARTMENT OF ELECTRICAL ENGINEERING FACULTY OF ENGINEERING AND TECHNOLOGY
JAMIA MILLIA ISLAMIA NEW DELHI-110025
CERTIFICATE
This is to certify that the major Project titled “AUTOMATIC CONTROL OF STREET
LIGHT” submitted in partial fulfillment of the requirements for the award of the degree
of Bachelor of Technology in Electrical Engineering by Malik Sameeullah (08EES-31),
Muneeb Ahmed (08 EES-50) & Rizwanullah Ansari (08EES-62) is a bonafide record
of the candidate‘s own work carried out by them under my supervision and guidance.
This work has not been submitted earlier in any university or institute for the award of any
degree to the best of my knowledge.
[Project Supervisor]
DR. TARIKUL ISLAM
Associate Professor
Dept. of Electrical Engineering
Jamia Millia Islamia
New Delhi-110025
Prof. ZAHEERUDIN (HOD)
Department of Electrical Engineering
Jamia Millia Islamia
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ACKNOWLEDGEMENT
We first thank our parents who gave us the moral support right from the moment
we thought about this project and who have provided us with opportunity to serve
the society as engineers
We express our sincere thanks to Prof. Zaheeruddin, Head of the Department of
Electrical Engineering for his work & cooperation to facilitate smooth progress of
the project.
We express our sincere thanks to our project guide Dr. Tarikul Islam for his
constant support, motivation and encouragement without which it would have been
very difficult for us to complete the project. He gave us the freedom to think and
made open all the resources he had in his personal capacity.
We would also like to thank Lab Assistants, Mr. Lokesh Kumar who is a Phd
scholars for his constant support and motivation and our friends for their constant
support, sacrifice and their encouragement.
Above all we would like to thank the almighty God for everything he has bestowed
on us.
MALIK SAMEEULLAH
MUNEEB AHMED
RIZWANULLAH ANSARI
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TABLE OF CONTENTS PAGE No.
ACKNOWLEDGEMENT iii
Abstract
CHAPTER 1: INTRODUCTION 1-2
CHAPTER 2:TECHNICAL REVIEW 3-9
2.1 Thyristor and its conduction
2.2 Line commutated converters
2.3 Necessity of getting synchronizing pulses
2.4 Popular methods of generating firing pulses
2.5 Basic building blocks
2.6 Block diagram representation of cosine control
CHAPTER 3: TECHNICAL LITERATURE REVIEW 10-40
3.1 Thyristor
3.2 Typical Thyristor characteristic
3.3 Firing Technique of Thyristor
3.4 Basic building Blocks
3.5 Unijunction Transistor
3.6 Triac
3.7 Op Amp
3.8 Firing Pulse technique
3.9 Transistor as a Switch
3.10 The 555 Timer
3.11 light dependent resistor
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3.12 Optocoupler
3.13 DC supply system
3.14 Street light
CHAPTER 4: PROPOSED PROJECT WORK 41-52
4.1 Synchronizing part
4.2 Cosine wave generator
4.3 Comparator for producing variable width pulse
4.4 Automatic variable voltage generator
4.5 Automatic on off circuit
4.6 Triac firing circuit
CHAPTER 5: CONCLUSION 53
5.1 Summary of the work reported in the project
5.2 Scope of future work
APPENDIX
REFERENCES
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ABSTRACT The theme of the project is to design the automatic control of street light with change of the
intensity of sunlight i.e.as the intensity of sunlight decreases, intensity of street light increases. LDR
is used to detect light intensity. Once there is enough darkness, circuit will turn on. Triac controlled
circuit is used to control the intensity of light. In this project there is the necessity of getting
synchronized firing pulses for the gate of the thyristor. Out of many variety of firing circuits
available, cosine controls scheme is used. In this interesting scheme, the supply voltage is first
integrated to obtain a cosine wave. The cosine wave so obtained is compared with a reference D.C
voltage. Therefore square pulses will be generated at the output terminal of the comparator. The
signal at output terminal is synchronized with the pulse and is delayed from the supply zero
crossing by an angle α. Instrumentation Op amp is used to provide a reference voltage to a firing
circuit. And this reference voltage is totally dependent on LDR resistance whose value change with
intensity of light.
This circuit is analysed and tested in various conditions and it provides absolute results which
shows the reliability of this circuit. Usually street light remain ON in morning time due to manual
operation, which cause loss of energy and therefore this project is very beneficial for saving power
and energy by automatic control. This circuit also provides the idea of developing the driver circuit
of LED lamp which is widely used nowadays.
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CHAPTER 1
INTRODUCTION
The main consideration in the present field technologies are automation, power consumption and
cost effectiveness. Automation is intended to reduce manpower with the help of intelligent systems.
Power saving is the main consideration forever as the source of the power (thermal, hydro etc.,) are
getting diminished due to various reasons. The main aim of the project is automatic street power
saving system with LDR; this is to save the power. We want to save power automatically instead of
doing manual. So it‘s easy to make cost effectiveness. This saved power can be used in some other
cases. So in villages, towns etc we can design intelligent systems for the usage of street lights.
Block diagram to implement circuit is shown in below figure.
MERITS AND DEMERITS OF OUR PROJECT:
In recent years the energy crisis has become one problem which the whole world must confront.
Home power consumption makes up the largest part of energy consumption in the world. In
particular, the power consumption of lamps in a typical home is a factor which can‘t be ignored.
The typical user needs different light intensities in different places. Sometimes the light intensity
from outside is sufficient, and thus we don‘t need to turn on any light. But sometimes the user
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leaves the room but forgets to turn off the light. These factors cause energy wastage. Therefore
some power management of light control in a home is necessary in order to save energy. Lights are
usually controlled by on/off switches. Of course, the user can switch a light on or off remotely by
connecting a specific device to a PC, but there has to be at least a PC, consuming a rather large
amount of power 24 hours a day, for the control mechanism. Moreover, this inconvenient practice
comes at a high cost for the user. In some designs one must install specific hardware and software
to control the lights, resulting in unacceptable costs. Furthermore this type of system cannot detect
either the temperature of the human body or light intensity of room.
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CHAPTER 2 TECHNICAL REVIEW
Thyristors or Silicon Controlled Rectifiers (SCRs) are widely used as a switching device in the
medium and large power levels starting from few kilowatts to several mega watts at voltage levels
of few hundred to several kilo volt levels. Bipolar Junction Transistors (BJTs) and Metal Oxide
Semiconductor Field Effect Transistors (MOSFETs) although have very fast switching
characteristics compared to SCRs, their uses are limited to medium power levels at few hundred
volts.
2.1 THYRISTOR & ITS CONDUCTION
A thyristor or SCR is a four layer device having three junctions J1, J2 and J3. Essentially three
terminals named anode, cathode and gate. Thyristor will be in reverse blocking mode if VAK < 0,
irrespective of the fact that a gate pulse is present or not. On the other hand the thyristor is said to
be in the forward blocking mode, when VAK > 0 in absence of any gate pulse, some current will
flow through the thyristor. In case of the thyristor is turning on either by exceeding the forward
break-over voltage or by applying a gate pulse between gate and cathode, called forward conduction
mode.
Fig 2.1 Symbol of diode and thyristor
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2.2 LINE COMMUTATED CONVERTERS
Conversion of line frequency (50 Hz) a.c. to d.c. is carried out either by using a single phase bridge
converter using four thyristors or 3-phase converter using six thyristors. A single phase fully
controlled bridge with four thyristor. With reference to the single phase converter circuit shown in
Fig.2.2 , we note that when B or positive, two diagonally opposite thyristors T and T are
forward biased and other two thyristors T and T are reversed biased. Therefore during intervals
i.e. to gate pulses are simultaneously applies to T and T , both start conducting and load
voltage = and also T3 and T4 are reversed biased and cannot conduct at that period of time
and vice versa.
Fig 2.2 Fully controlled converter
2.3 NECESSITY OF GETTING SYNCHRONIZING PULSES
For T and T , α is to be measured from the instant when is zero and going towards positive.
Similarly T and T , α is to be measured from the instant is zero and going towards positive.
Thus we see that for successful operation of the fully controlled bridge, the gate pulses to be
properly synchronized with the a.c. power supply. It is noted that each thyristor conducts for
only.
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Fig. 2.3 Typical waveform of single phase inverter
2.4 POPULAR METHODS OF GENERATING FIRING PULSES
1) Using ramp signal: In this scheme a ramp signal is generated in synchronism with the a.c.
supply. The first comparator translates the input sinusoidal voltage into a square wave voltage.
When the square wave voltage is high, the transistor (P-N-P type) collector-base junction is
forward biased; the transistor is non conducting stage (off) and the capacitor charges
exponentially giving ramp rise of the voltage at the output. However, as soon as the square
voltage is negative, transistor becomes on due to collector-base junction is reverse biased and
the capacitor discharges sharply giving a saw tooth like waveform as shown in Fig. 2.4.
Fig. 2.4 Basic idea of ramp scheme
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This triangular voltage can now be compared by the second comparator with a variable
reference d.c. voltage ref to get the firing pulse signal at . The value of α can be varied in
the range α by changing the value of the reference voltage (Vref).
2). Using cosine control: In this interesting scheme, the supply voltage Vs is first integrated to
obtain a cosine wave as shown in Fig. 2.5. The cosine wave so obtained is compared with a
reference d.c. voltage (Vref). Therefore square pulses will be generated at the output terminal
of the comparator. The signal at is synchronized with the pulse and is delayed from the
supply zero crossing by an angle α. Obviously, the value of α can be varied a range of α
.
Fig 2.5 basic idea of cosine scheme
2.5 BASIC BUILDING BLOCKS
Basic blocks which will be necessary to implement any firing control scheme in a converter circuit
are shown in Fig.2.6. The figure demonstrates with the help of a single line diagram, the major
blocks necessary to generate firing pulses for any scheme. The converter is organized from a.c.
power. Since the firing pulses must be synchronized with the a.c. supply, a.c. power also goes to the
isolation and synchronizing blocks. Isolation is essential as because the control circuit uses very
low power devices such as various chips, logic gates etc.
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Fig 2.6 Basic block of firing control circuit
The logic circuit block uses few logic gates to implement a particular firing scheme. The strength of
the pulse obtained from logic gates may not be sufficient to drive the gate of a thyristor, so
amplification of the pulse along with isolation is used at final stage.
2.6 BLOCK DIAGRAM REPRESENTATION OF THE COSINE
The emphasis of this paper is the implementation of cosine control scheme. We shall first outline
the scheme in terms of block diagram and then explain each block in detail. Let be the supply
voltage feeding the converter for which the control pulses are to be generated. With the help of a
step down centre tapped transformer, is transformed into two power level voltage and .
T1 & T2 are to be fired when Va0 is positive and T3 & T4 are to be fired when is positive. For
T & T the firing angle α is to be measured from the instant when a is zero and increasing in
the positive direction. The range of variation of α is to . Similarly for T & T the firing angle
α is to be measured from the instant when b is zero and increasing in the positive direction. Basic
idea for generating necessary pulses for T1 & T2 and T3 & T4 can be understood by referring
figures 2.7 and 2.8.
With reference to Fig. 8 the signal Va0 is integrated with the help of Integrator -1 and a cosine
wave will be obtained. This cosine wave is compared with a variable d.c. voltage Vr using a
comparator-1. Noting that Vr is connected to the +ve terminal of the comparator-1, the output of the
comp-1 will be square wave and it goes to high state from the instant when Vr becomes greater than
the cosine voltage value. However the width of the pulse will vary as Vr is varied. Our first aim will
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be to make the width of the pulse to be . This is achieved in the following way. The output of
the comp- is fed to a block mono- . Output of the mono will be a pulse of small width at positive
going edge of the input square wave. The output of mono- will thus give small pulses separated by
. Noting that Vr is connected to the +ve terminal of the comparator-1, the output of the comp-1
will be square wave and it goes to high state from the instant when Vr becomes greater than the
cosine voltage value. However the width of the pulse will vary as r is varied. Our first aim will be
to make the width of the pulse to be . This is achieved in the following way. The output of the
comp-1 is fed to a block mono-1. Output of the mono will be a pulse of small width at positive
going edge of the input square wave. The output of mono- will thus give small pulses separated by
.
Fig. 2.7 Basic Block of control scheme
The voltage Vb0 is similarly processed, i.e., it is integrated then compared with the same variable
d.c. with the help of comparator-2, output of OMP- will be a square wave and will be shifted by
from the output square wave of OMP-1. This is because of the fact that Vb0 lags Va0 by .
The output of the comp-2 is now fed to a block mono-2. Output of mono-2 will be a pulse of small
width at positive going edge of the input square wave. The output of mono-2 will thus give small
pulses separated by .
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Fig. 2.8: Wave form at different point of ckt. of fig 2.7
This is important to know that the fixed width pulse waveforms at the output of mono- and mono-
are shifted by as shown in Fig. 2.8. The outputs of mono1 and mono-2 can be used in
conjunction with to two S-R flip flops so as to generate two square waves each having a fixed width
of and mutually separated by . By some modification this technique can be used for
voltage control.
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CHAPTER 3
LITERATURE REVIEW
3.1 THYRISTOR:
Thyristors or silicon controlled rectifiers (SCR) are finding many uses in electronics, and in
particular for power control. Thyristors or silicon controlled rectifiers( SCRs) have even been called
the workhorse of high power electronics. The thyristor is a four-layered, three terminal
semiconducting devices, with each layer consisting of alternately N-type or P-type material, for
example P-N-P-N. The main terminals, labelled anode and cathode, are across the full four layers,
and the control terminal, called the gate, is attached to p-type material near to the cathode. (A
variant called an SCS—Silicon Controlled Switch—brings all four layers out to terminals.) The
operation of a thyristor can be understood in terms of a pair of tightly coupled bipolar junction
transistors, arranged to cause the self-latching action.
Fig. 3.1 Structure on the physical and electronic level, and the thyristor symbol.
3.2 TYPICAL THYRISTOR CHARACTERISTICS:
Figure 3.2 shows a typical characteristic curve for a thyristor. It can be seen that in the reverse
biased region it behaves in a similar way to a diode. All current, apart from a small leakage current
is blocked (reverse blocking region) until the reverse breakdown region is reached, at which point
the insulation due to the depletion layers at the junctions breaks down.
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In the forward biased mode, unlike a normal diode, no current apart from a small leakage current
flows. This is called the forward blocking mode. If a gating pulse is applied however, the thyristor
"fires" and the forward resistance of the device falls to a very low value, allowing very large
(several amperes) currents to flow in the forward conducting mode. Thyristors can also be made to
fire by applying a very large forward voltage between anode and cathode, but this is not desirable as
the device is not then being used to control conduction.
Fig. 3.2 Characteristics of SCR.
3.3 FIRING TECHNIQUE OF THYRISTOR:
An SCR can be switched from off state to on state in several ways and these are: forward voltage
triggering, temperature triggering, light triggering and gate triggering. Gate triggering is, however,
the most common method of turning on the SCRs, because this method lends itself accurately for
turning on the SCR at the desired instant of time. In addition gate triggering is an efficient and
reliable method.
3.4 BASIC BUILDING BLOCKS:
Basic blocks which will be necessary to implement any firing control scheme in a converter circuit
are shown in Fig. 3.3. The figure demonstrates with the help of a single line diagram, the major
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blocks necessary to generate firing pulses for any scheme. The converter is organized from a.c.
power. Since the firing pulses must be synchronized with the a.c. supply, a.c. power also goes to the
isolation and synchronizing blocks. Isolation is essential as because the control circuit uses very
low power devices such as various chips, logic gates etc. The logic circuit block uses few logic
gates to implement a particular firing scheme. The strength of the pulse obtained from logic gates
may not be sufficient to drive the gate of a thyristor, so amplification of the pulse along with
isolation is used at final stage as shown Fig. 3.3.
Fig. 3.3 Basic block of firing control circuit.
3.5 UNIJUNCTION TRANSISTOR:
Although a unijunction transistor is not a thyristor, this device can trigger larger thyristors with a
pulse at base B1. A unijunction transistor is composed of bar of N-type silicon having a P-type
connection in the middle. See Figure 3.4(a). The connections at the ends of the bar are known as
bases B1 and B2; the P-type mid-point is the emitter. With the emitter disconnected, the total
resistance RBBO, a datasheet item, is the sum of RB1 and RB2 as shown in Figure 3.4(b). RBBO ranges
from 4- kΩ for different device types. The intrinsic standoff ratio η is the ratio of RB1 to RBBO. It
varies from 0.4 to 0.8 for different devices. The schematic symbol is Figure 3.4(c).
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Fig 3.4 Symbol and formula of UJT
The Unijunction emitter current vs voltage characteristic curve (Figure 3.5 (a)) shows that as
VE increases, current IE increases up IP at the peak point. Beyond the peak point, current increases
as voltage decreases in the negative resistance region. The voltage reaches a minimum at the valley
point. The resistance of RB1, the saturation resistance is lowest at the valley point.
IP and IV, are datasheet parameters; for a 2n2647, IP and IV are 2µA and 4mA,
respectively. [AMS] VP is the voltage drop across RB1 plus a 0.7V diode drop; see Figure 3.5 (b).
VV is estimated to be approximately 10% of VBB.
Fig 3.5 V-I characteristic of UJT
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The relaxation oscillator in Figure 3.6 below is an application of the unijunction oscillator. RE
charges CE until the peak point. The unijunction emitter terminal has no effect on the capacitor until
this point is reached. Once the capacitor voltage, VE, reaches the peak voltage point VP, the lowered
emitter-base1 E-B1 resistance quickly discharges the capacitor. Once the capacitor discharges
below the valley point VV, the E-RB1 resistance reverts back to high resistance, and the capacitor is
free to charge again.
Fig.3.6 Unijunction transistor relaxation oscillator and waveforms.
3.6 TRIAC:
Triac is an electronic component that can conduct current in either direction when it is triggered
(turned on), and is formally called a bidirectional triode thyristor or bilateral triode thyristor.
Triacs belong to the thyristor family and are closely related to Silicon-controlled rectifiers (SCR).
However, unlike SCRs, which are unidirectional devices (i.e. can conduct current only in one
direction), TRIACs are bidirectional and so current can flow through them in either direction.
Another difference from SCRs is that TRIACs can be triggered by either a positive or a negative
current applied to its gate electrode, whereas SCRs can be triggered only by currents going into the
gate. In order to create a triggering current, a positive or negative voltage has to be applied to the
gate with respect to the A1 terminal (otherwise known as MT1).
Once triggered, the device continues to conduct until the current drops below a certain threshold,
called the holding current.
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The bidirectionality makes TRIACs very convenient switches for AC circuits, also allowing them to
control very large power flows with milliampere-scale gate currents. In addition, applying a trigger
pulse at a controlled phase angle in an AC cycle allows one to control the percentage of current that
flows through the TRIAC to the load (phase control), which is commonly used, for example, in
controlling the speed of low-power induction motors, in dimming lamps and in controlling AC
heating resistors.
Fig. 3.7 Triac
3.7 OP AMP:
An op amp is a very high gain differential amplifier with high input impedance and low output
impedance. Typical uses of the op amp are to be providing voltage amplitude changes, oscillator,
filters circuit and many type of instrumental circuit.
3.7.1 INVERTING AMPLIFIER
The Open Loop Gain of an ideal operational amplifier can be very high, as much as 1,000,000
(120dB) or more. However, this very high gain is of no real use to us as it makes the amplifier both
unstable and hard to control as the smallest of input signals, just a few micro-volts, μ would be
enough to cause the output voltage to saturate and swing towards one or the other of the voltage
supply rails losing complete control. As the open loop DC gain of an operational amplifier is
extremely high we can therefore afford to lose some of this gain by connecting a suitable resistor
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across the amplifier from the output terminal back to the inverting input terminal to both reduce and
control the overall gain of the amplifier. This then produces and effect known commonly
as Negative Feedback, and thus produces a very stable Operational Amplifier based system.
Negative Feedback is the process of "feeding back" a fraction of the output signal back to the input,
but to make the feedback negative, we must feed it back to the negative or "inverting input"
terminal of the op-amp using an external Feedback Resistor called Rf. This feedback connection
between the output and the inverting input terminal forces the differential input voltage towards
zero. This effect produces a closed loop circuit to the amplifier resulting in the gain of the amplifier
now being called its Closed-loop Gain. A closed-loop amplifier uses negative feedback to
accurately control the overall gain but at a cost in the reduction of the amplifiers bandwidth.
This negative feedback results in the inverting input terminal having a different signal on it than the
actual input voltage as it will be the sum of the input voltage plus the negative feedback voltage
giving it the label or term of a Summing Point. We must therefore separate the real input signal
from the inverting input by using an Input Resistor, Rin. As we are not using the positive non-
inverting input this is connected to a common ground or zero voltage terminal as shown below, but
the effect of this closed loop feedback circuit results in the voltage potential at the inverting input
being equal to that at the non-inverting input producing a Virtual Earth summing point because it
will be at the same potential as the grounded reference input. In other words, the op-amp becomes a
"differential amplifier".
3.7.2 INVERTING AMPLIFIER CONGIGURATION:
Fig 3.8 Inverting Amplifier
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In this Inverting Amplifier circuit the operational amplifier is connected with feedback to produce a
closed loop operation. For ideal op-amps there are two very important rules to remember about
inverting amplifiers, these are: "no current flows into the input terminal" and that "V1 equals V2",
(in real op-amps both these rules are broken). This is because the junction of the input and feedback
signal (X) is at the same potential as the positive (+) input which is at zero volts or ground then, the
junction is a ― irtual Earth". Because of this virtual earth node the input resistance of the amplifier
is equal to the value of the input resistor, Rin and the closed loop gain of the inverting amplifier can
be set by the ratio of the two external resistors.
We said above that there are two very important rules to remember about Inverting Amplifiers or
any operational amplifier for that matter and these are.
3.7.3 NON INVERTING AMPLIFIER:
The second basic configuration of an operational amplifier circuit is that of a Non-inverting
Amplifier. In this configuration, the input voltage signal, (Vin) is applied directly to the non-
inverting (+) input terminal which means that the output gain of the amplifier becomes "Positive" in
value in contrast to the "Inverting Amplifier" circuit whose output gain is negative in value. The
result of this is that the output signal is "in-phase" with the input signal.
Feedback control of the non-inverting amplifier is achieved by applying a small part of the output
voltage signal back to the inverting (-) input terminal via an Rf - R2 voltage divider network, again
producing negative feedback. This closed-loop configuration produces a non-inverting amplifier
circuit with very good stability, a very high input impedance, Rin approaching infinity, as no
current flows into the positive input terminal, (ideal conditions) and a low output
impedance, Rout as shown below.
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Fig. 3.9
3.7.4 OP-AMP INTEGRATOR AMPLIFIER:
An operational amplifier can be used as part of a positive or negative feedback amplifier or as an
adder or subtractor type circuit using just pure resistances in both the input and the feedback loop.
But what if we were to change the purely resistive (Rf) feedback element of an inverting amplifier
to that of a frequency dependant impedance, (Z) type complex element, such as a capacitor, C. By
replacing this feedback resistance with a capacitor we now have an RC network across the
operational amplifier producing an Op-amp Integrator circuit as shown below.
Fig 3.10 Integrator
As its name implies, the Op-amp Integrator is an operational amplifier circuit that performs the
mathematical operation of integration that is we can cause the output to respond to changes in the
input voltage over time. The integrator amplifier acts like a storage element that ―produces a
voltage output which is proportional to the integral of its input voltage with respect to time‖. In
other words the magnitude of the output signal is determined by the length of time a voltage is
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present at its input as the current through the feedback loop charges or discharges the capacitor as
the required negative feedback occurs through the capacitor.
When a voltage, Vin is firstly applied to the input of an integrating amplifier, the uncharged
capacitor C has very little resistance and acts a bit like a short circuit (voltage follower circuit)
giving an overall gain of less than one. No current flows into the amplifiers input and point X is a
virtual earth resulting in zero output. As the feedback capacitor C begins to charge up, its
reactance Xc decreases this results in the ratio of Xc/Rin increasing producing an output voltage
that continues to increase until the capacitor is fully charged.
At this point the capacitor acts as an open circuit, blocking anymore flow of DC current. The ratio
of feedback capacitor to input resistor (Xc/Rin) is now infinite resulting in infinite gain. The result
of this high gain (similar to the op-amps open-loop gain), is that the output of the amplifier goes
into saturation as shown below. (Saturation occurs when the output voltage of the amplifier swings
heavily to one voltage supply rail or the other with little or no control in between).
Fig 3.11
The rate at which the output voltage increases (the rate of change) is determined by the value of the
resistor and the capacitor, ―RC time constant‖. By changing this RC time constant value, either by
changing the value of the Capacitor, C or the Resistor, R, the time in which it takes the output
voltage to reach saturation can also be changed for example.
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Fig. 3.12
If we apply a constantly changing input signal such as a square wave to the input of an integrator
amplifier then the capacitor will charge and discharge in response to changes in the input signal.
This results in the output signal being that of a sawtooth waveform whose frequency is dependent
upon the RC time constant of the resistor/capacitor combination. This type of circuit is also known
as a Ramp Generator and the transfer function is given below.
Fig. 3.13
3.8 FIRING PULSE TECHNIQUE:
3.8.1 RESISTANCE TRIGGERING:
A simple firing triggering circuit is shown in fig. 3.14. the rsistance R1 limit the current through the
gate of the SCR. R2 is a variable resistance added to the circuit to achieve control over the
triggering angle of SCR. Resistor R is a stabilizing resistor. The diode D is required to ensure that
no negative voltage reaches the gate of the SCR.
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Fig 3.14 R firing circuit and waveform
3.8.2 RESISTANCE CAPACITIVE TRIGERRING:
The capacitor C in the circuit is connected to shift the phase of the gate voltage. D1 is used to
prevent negative voltage from reaching the gate cathode of SCR.
In the negative half cycle capacitor charge to the peak negative voltage of the supply (-V) through
the diode D2. Capacitor maintains this negative voltage until supply voltage cross zero. As the
supply become positive, the capacitor charge through resistor ‗R‘ from initial voltage of –Vm to a
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positive value. When the capacitor voltage is equal to the gate trigger voltage of the SCR, SCR is
fired and capacitor voltage is clamped to a small positive value.
Fig. 3.15. Basic idea of RC control scheme.
3.9 TRANSISTOR AS A SWITCH:
Fig. 3.16 Transistor used as a switch
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The circuit resembles that of the common emitter. The difference is that to operate the transistor as
a switch the transistor needs to be turned either fully "OFF" (cut-off) or fully "ON" (saturated). An
ideal transistor switch would have infinite circuit resistance between the Collector and Emitter
when turned "fully-OFF" resulting in zero current flowing through it and zero resistance between
the Collector and Emitter when turned "fully-ON", resulting in maximum current flow. In practice
when the transistor is turned "OFF", small leakage currents flow through the transistor and when
fully "ON" the device has a low resistance value causing a small saturation voltage (VCE) across it.
Even though the transistor is not a perfect switch, in both the cut-off and saturation regions the
power dissipated by the transistor is at its minimum. In order for the base current to flow, the base
input terminal must be made more positive than the emitter by increasing it above the 0.7 volts
needed for a silicon device. By varying this base-emitter voltage VBE, the base current is also
altered and which in turn controls the amount of collector current flowing through the transistor as
previously discussed. When maximum collector current flows the transistor is said to be saturated.
The value of the base resistor determines how much input voltage is required and corresponding
base current to switch the transistor fully "ON".
3.10 THE 555 TIMER:
The 555 timer is an integrated circuit (chip) implementing a variety of timer and multivibrator
applications. It was produced by Signe tics Corporation in early 1970. The original name was the
SE555/NE555 and was called "The IC Time Machine". The 555 gets its name from the three 5-KΩ
resistors used in typical early implementations. It is widely used because of its ease to use, low
price and reliability.
It is one of the most popular and versatile integrated circuits which can be used to build lots of
different circuits. It includes 23 transistors, 2 diodes and 16 resistors on a silicon chip installed in an
8-pin mini dual-in-line package (DIP-8)(Refer to Figure 3.17).
The 555 Timer is a monolithic timing circuit that can produce accurate and highly stable time
delays or oscillations. The timer basically operates in one of the two modes—monostable (one-shot)
multivibrator or as an astable (free-running) multivibrator. In the monostable mode, it can produce
accurate time delays from microseconds to hours. In the astable mode, it can produce rectangular
waves with a variable duty cycle. Frequently, the 555 is used in astable mode to generate a
continuous series of pulses, but you can also use the 555 to make a one-shot or monostable circuit.
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The 555 can source or sink 200 mA of output current, and is capable of driving wide range of
output devices. The output can drive TTL (Transistor-Transistor Logic) and has a temperature
stability of 50 parts per million (ppm) per degree Celsius change in temperature, or equivalently
0.005 %/°C.
Applications of 555 timer in monostable mode include timers, missing pulse detection, bounce free
switches, touch switches, frequency divider, capacitance measurement, pulse width modulation
(PWM) etc.
In astable or free running mode, the 555 can operate as an oscillator. The uses include LED and
lamp flashers, logic clocks, security alarms, pulse generation, tone generation, pulse position
modulation, etc. In the bistable mode, the 555 can operate as a flip-flop and is used to make
bounce-free latched switches, etc.
Refer to Figure 3.17 for the brief description of the pin connections. The pin numbers used refer to
the 8-pin mini DIP and 8-pin metal can packages. The 555 can be used with a supply voltage
(VCC) in the range 4.5 to 15V (18V absolute maximum).
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Fig. 3.17 Functional Block Diagram of 555 Timer
The working of 555 timer is described using its functional block diagram. As shown in Figure 3.18,
the 555 timer consists of a voltage divider arrangement, two comparators, an RS flip-flop, an n-p-n
transistor Q1 and a p-n-p transistor Q2. Since the voltage divider has equal resistors, the upper
comparator has a trip point of
UTP = 2/3 Vcc
The comparator 2 has a trip point of
LTP = 1/3 Vcc
As seen in the Figure 3.18, the pin 6 (Threshold) is connected to the comparator 1. This voltage
comes from the external components (not shown). When the threshold is greater than the UTP, the
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comparator 2 has a high output. Pin 2 (trigger) is connected to the comparator 2. This is the trigger
voltage that is used for the monostable operation of the 555 timer. When the trigger is inactive, the
trigger voltage is high. When the trigger voltage falls to less than the LTP, comparator 2 produces a
high output.
3.10.1 ASTABLE MULTIVIBRATOR:
The application of 555 timer as an astable multivibrator. An astable multivibrator is a wave-
generating circuit in which neither of the output levels is stable. The output keeps on switching
between the two unstable states and is a periodic, rectangular waveform. The circuit is therefore
known as an ‗astable multivibrator‘. lso, no external trigger is required to change the state of the
output, hence it is also called ‗free-running multivibrator‘. The time for which the output remains in
one particular state is determined by the two resistors and a capacitor externally connected to the
555 timer.
Figure 3.19 shows 555 timer connected as an astable multivibrator. Pin 5 is bypassed to ground
through a . μF capacitor. The power supply + is connected to common of pin 4 and pin 8
and pin 1 is grounded. If the output is high initially, capacitor C starts charging towards through RA
and RB. As soon as the voltage across the capacitor becomes equal to 3/2 Vcc, the upper
comparator triggers the flip-flop, and the output becomes low. The capacitor now starts discharging
through RB and transistor Q1. When the voltage across the capacitor becomes 1/3Vcc, the output of
the lower comparator triggers the flip-flop and the output becomes high. The cycle then repeats.
The output voltage and capacitor voltage waveforms are shown in Figure 3.19.
Fig. 3.18 Circuit diagram for Astable Multivibrator
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Fig. 3.19 Output voltage waveforms
3.11 LIGHT DEPENDENT RESISTOR:
A transducer is a device that converts energy from one form to another. In the control system a
photoconductive cell is used as a transducer. Electrical conduction in semiconductor materials
occurs when free charge carrier, e.g. electrons, is available in the material and an electric field is
applied. In certain semiconductors when light energy strike on them in correct order of magnitude,
they release charge carriers.
Source Illumination chart
S.No Light Source Illumination (Lux)
1. Moonlight 0.1
2. 60W bulb at 1m 50
3. Fluorescent light 500
4. Bright sunlight 30000
This increases flow of current produced by an applied voltage. The increase of current with increase
in light intensity and the applied voltage is constant. It means that the resistance of semiconductors
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decreases with increase the light intensity. Therefore, these semiconductors are called
photoconductive cells or photo resistors or Light Dependent Resistors (LDR), since incident light
effectively varies their resistance (Figure 2.3). In bright light the resistance of the cell can be as low
as 80 ohm. When the cell is kept in darkness its resistance is called dark resistance. At 50 LUX
(darkness) the resistance increases to over 1M ohm. The dark resistance may be as high as
× Ω.
Fig 3.22 LDR and its characteristic graph
A photoconductor has a relatively large sensitive area. A small change in light intensity causes a
large change in resistance. It is common for a photoconductive element to exhibit a resistance
change of 1000:1 for a dark to light irradiance change of 5×10-3 W/m2 to 50 W/m2. The
relationship between irradiance and resistance is, however, not linear. It is closely an exponential
relationship. The photoconductive cell suffers from a major disadvantage that temperature change
causes substantial resistance changes for a particular light intensity.
3.12 OPTOCOUPLER:
An Optocoupler, also known as an Opto-isolator or Photo-coupler, are electronic components
that interconnect two electrical circuits by means of an optical interface. The basic design of an
optocoupler consists of an LED that produces infra-red light and a semiconductor photo-sensitive
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device that is used to detect this emitted infra-red light. Both the LED and photo-sensitive device
are enclosed in a light-tight body or package with metal legs for the electrical connections as
shown.
An optocoupler or opto-isolator consists of a light emitter, the LED and a light sensitive receiver
which can be a single photo-diode, photo-transistor, photo-resistor, photo-SCR, or a photo-TRIAC
and the basic operation of an optocoupler is very simple to understand.
Fig. 3.22
3.12.1 PHOTO-TRANSISTOR OPTOCOUPLER:
Assume a photo-transistor device as shown. Current from the source signal passes through the input
LED which emits an infra-red light whose intensity is proportional to the electrical signal. This
emitted light falls upon the base of the photo-transistor, causing it to switch-ON and conduct in a
similar way to a normal bipolar transistor. The base connection of the photo-transistor can be left
open for maximum sensitivity or connected to ground via a suitable external resistor to control the
switching sensitivity making it more stable.
When the current flowing through the LED is interrupted, the infra-red emitted light is cut-off,
causing the photo-transistor to cease conducting. The photo-transistor can be used to switch current
in the output circuit. The spectral response of the LED and the photo-sensitive device are closely
matched being separated by a transparent medium such as glass, plastic or air. Since there is no
direct electrical connection between the input and output of an optocoupler, electrical isolation up to
10kV is achieved.
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Fig. 3.23 Photo-Transistor Optocoupler
3.12.2 OPTOCOUPLER TYPES:
Optocoupler are available in four general types, each one having an infra-red LED source but with
different photo-sensitive devices. The four optocoupler are: photo-transistor, photo-
darlington, photo-SCR and photo-triac as shown below.
Fig. 3.24
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The photo-transistor and photo-darlington devices are mainly for use in DC circuits while the
photo-SCR and photo-triac allow AC powered circuits to be controlled. There are many other kinds
of source-sensor combinations, such as LED-photodiode, LED-LASER, lamp-photo resistor pairs,
reflective and slotted optocoupler.
Simple home made optocoupler can be constructed by using individual components. An LED and a
photo-transistor are inserted into a rigid plastic tube or encased in heat-shrinkable tubing as shown.
The tubing can be of any length.
Fig. 3.25
3.12.3 OPTOCOUPLER APPLICATIONS:
Optocoupler and opto-isolators can be used on their own, or to switch a range of other larger
electronic devices such as transistors and triacs providing the required electrical isolation between a
lower voltage control signal and the higher voltage or current output signal. Common applications
for optocoupler include microprocessor input/output switching, DC and AC power control, PC
communications, signal isolation and power supply regulation which suffer from current ground
loops, etc. The electrical signal being transmitted can be either analogue (linear) or digital (pulses).
3.12.4 OPTOCOUPLER TRIAC CONTROL:
This type of optocoupler configuration forms the basis of a very simple solid state relay application
which can be used to control any AC mains powered load such as lamps and motors. Also unlike a
thyristor (SCR), a triac is capable of conducting in both halves of the mains AC cycle with zero-
crossing detection.
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Fig. 3.26
3.13 DC SUPPLY SYSTEM
When four diodes are connected as shown in converter circuit, the circuit is called a BRIDGE
RECTIFIER. The input to the circuit is applied to the diagonally opposite corners of the network,
and the output is taken from the remaining two corners.
One complete cycle of operation will be discussed to help you understand how this circuit works.
Let us assume the transformer is working properly and there is a positive potential at point A and a
negative potential at point B. The positive potential at point A will forward bias D3 and reverse bias
D4. The negative potential at point B will forward bias D1 and reverse bias D2. At this time D3 and
D1 are forward biased and will allow current flow to pass through them; D4 and D2 are reverse
biased and will block current flow. The path for current flow is from point B through D1, up
through RL, through D3, through the secondary of the transformer back to point B. This path is
indicated by the solid arrows. Waveforms (1) and (2) can be observed across D1 and D3.
One-half cycle later the polarity across the secondary of the transformer reverses, forward biasing
D2 and D4 and reverse biasing D1 and D3. Current flow will now be from point A through D4, up
through RL, through D2, through the secondary of T1, and back to point A. This path is indicated by
the broken arrows. Waveforms (3) and (4) can be observed across D2 and D4. You should have
noted that the current flow through RL is always in the same direction. In flowing through RL this
current develops a voltage corresponding to that shown in waveform (5). Since current flows
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through the load (RL) during both half cycles of the applied voltage, this bridge rectifier is a full-
wave rectifier.
One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given
transformer the bridge rectifier produces a voltage output that is nearly twice that of the
conventional full-wave circuit. This may be shown by assigning values to some of the components
shown in views A and B of figure. Assume that the same transformer is used in both circuits. The
peak voltage developed between points X and Y is 1000 volts in both circuits. In the conventional
full-wave circuit shown in view A, the peak voltage from the center tap to either X or Y is 500
volts. Since only one diode can conduct at any instant, the maximum voltage that can be rectified at
any instant is 500 volts. Therefore, the maximum voltage that appears across the load resistor is
nearly - but never exceeds - 500 volts, as a result of the small voltage drop across the diode. In the
bridge rectifier shown in view B, the maximum voltage that can be rectified is the full secondary
voltage, which is 1000 volts. Therefore, the peak output voltage across the load resistor is nearly
1000 volts. With both circuits using the same transformer, the bridge rectifier circuit produces a
higher output voltage than the conventional full-wave rectifier circuit. Now output receive at a
terminal of bridge is ripple type and cannot directly use for dc supply. Now a very popular capacitor
filter circuit is used to provide constant DC output. This is a condition when no load is applied
across capacitor. When load is connected across capacitor, there is a little voltage ripple. Further
smoothing of DC output is done by various other techniques like RC filter, OP-AMP series
regulator, Series Voltage Regulator circuit etc.
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Fig 3.27 DC Rectifier circuit
Sometime, DC output which we receive is more than the required value and need to reduce the
level. Regulator IC units contain the circuitry for reference source, comparator amplifier, control
device and overload protection all in a single IC. IC units provide regulation of either a fixed
positive voltage, a fixed negative voltage, or an adjustable set voltage.
For making DC supply circuit, we use transformer of 230V/14-014V. This type of transformer
provide center tap for neutral point (0V). Dual power supply with 12V and -12V with neutral point
is obtained. There will be instances where the currents from each supply will be unequal. In this
cause voltage is different for each supply. This cause there is a chance of development of error. The
input DC is given a voltage divider to establish a "virtual earth", and this is used as the 0V reference
for the unit to be powered. In its simplest form, it uses a pair of resistors and two additional filter
caps to make sure that the hum is within the capability of opamps to reject. There will be instances
where the currents from each supply will be unequal. Where this is the case, the resistor divider is
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not sufficient, and the +ve and -ve voltages will be unequal. By using a cheap opamp (such as a
uA741), a DC imbalance between supplies of up to about 15mA will not cause a
problem. However, we can do better with a dual opamp (which will cost the same or less anyway),
and increase the capability for up to about 30mA of difference between the two supplies.
Fig 3.28 Circuit to produce balance neutral point
Fig 3.29 12 V dual supply
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3.14 STREET LIGHT
A Street light, lamppost, street lamp, light standard, or lamp standard is a raised source of light on
the edge of a road or walkway, which is turned on or lit at a certain time every night. Modern lamps
may also have light-sensitive photocells to turn them on at dusk, off at dawn, or activate
automatically in dark weather. In older lighting this function would have been performed with the
aid of a solar dial. It is not uncommon for street lights to be on posts which have wires strung
between them, such as on telephone poles or utility poles.
3.14.1 LED STREET LIGHT:
An LED street light is an integrated light that uses LEDs as its light source. These are considered
integrated lights because, in most cases, the luminaire and the fixture are not separate parts (except
LED Gine-based luminaires). New in manufacturing, the LED light cluster is sealed on a panel and
then assembled to the LED panel with a heat sink to become an integrated lighting fixture.
Fig. 3.30
3.14.2 SOLAR STREET LIGHT:
Solar energy is a renewable source of energy, which is long-lasting and no pollution type. It can be
easily utilized and also a cost effective in long term. Solar street light do not need staff for
management and control and it can easily stalled in public places like hospital, school, street etc.
LED lamp is generally used because of long life and energy saving (low watt). LED street lamp is
compact and shock resistive with energy efficient. Solar street lights are raised light sources which
are powered by photovoltaic panels generally mounted on the lighting structure. The photovoltaic
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panels charge a rechargeable battery, which powers a fluorescent or LED lamp during the night.
Various control circuit is designed which is compact and efficient.
Fig. 3.31
3.14.3 HIGH INTENSITY DISCHARGE LAMP:
High-intensity discharge lamps (HID lamps) are a type of electrical lamp which produces light by
means of an electric arc between tungsten electrodes housed inside a translucent or
transparent fused quartz or fused alumina arc tube. This tube is filled with both gas and metal salts.
The gas facilitates the arc‘s initial strike. Once the arc is started, it heats and evaporates the metal
salts forming a plasma, which greatly increases the intensity of light produced by the arc and
reduces its power consumption. High-intensity discharge lamps are a type of arc lamp.
Fig. 3.32
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Features:
1. High efficiency -105 lm/W
2. Long life up to 24000 hrs.
3. Bright light and excellent colour rendering
4. UV control
5. Two colour temperatures: 3000K and 42000K
6. Direct replacement of high pressure sodium and Quartz Metal Halide lamp
7. High range of wattage from 20 Watt to 400 Watt
3.14.4 CONTROL OF STREET LIGHT:
Manual switch is provided on each pole of street light or a central switch is provided for series of
street light for turn On/Off. This cause extra labour is required. Generally many cities used
automatic circuit to turn On/Off. This is possible using LDR circuit which helps to switch transistor
at specific time as it resistance change and activate relay to turn circuit on.
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CHAPTER 4 PROPOSED PROJECT WORK
Thyristor or Triac is a switching device in the medium and large power levels starting from few
kilowatts to several megawatts at voltage level of few hundred to several kilo volts levels.
BJT(Bipolar Junction Transistor) and MOSFETs (Metal Oxide Semiconductor Field Transistor)
also used as switching device at low voltage. We are working to design low cost digital firing
circuit with automatic control of firing angle according to light intensity. The circuit is designed
in such a manner so that firing circuit is active only in night (when necessary). Circuit is mainly
divided into part (1) On/Off switching circuit, (2) firing angle control circuit. Firing circuit is
divided into 10 parts as shown in fig. 4.1
Fig 4.1 Schematic Block Diagram
4.1 Synchronizing part: For producing proper firing pulse, it is necessary to synchronize the
circuit. A 220/6-0-6 V or 220/3-0-3 V 50 Hz control transformer is selected for stepping down
the 220 V supply to a low level.
Isolation &
Synchronizing block
Logic circuit
for pulse
generation
Amplification of
pulse and
isolation
LDR control circuit
(ON/OFF, and control of firing angle)
TRIAC Power
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4.2 Cosine wave generator
One of the very popular integrator circuit using Op amp can be used to produce cosine wave.
Fig 6.2 shows integrator circuit. Signal ∫ will be obtained.
Fig 4.2 Integrator circuit
One of the problem with this type of integrator when used in practical circuit is a reduction in
output amplitude, which is not good for our circuit. For this reason another simple phase shift
circuit fig 4.3 is used and phase shift of 90 degree is set using variable resistor. For this
configuration, cosine wave at output is found for potentiometer resistance of .7 kΩ.
Fig 4.3 Phase shifting circuit
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4.3 Comparator for producing variable width pulse
An OP AMP (LM 324) is used to realize the comparator block. The variable d.c voltage is
applied to the non-inverting terminal and cosine signal is applied at inverting terminal. Variable
voltage output is varied using simple variable pot technique. Firing angle control from 0 to 180
degree by varying variable voltage from 4.2 V to -4.2V.
Fig. 4.4 comparator circuit
4.4 Automatic Variable Voltage Generator
For automatic control of firing angle, it is necessary to make a circuit which generate variable
d.c voltage for comparator circuit according to the intensity of light (Variable voltage output
vary from -4.2 V to 4.2 V as darkness increase so, that firng angle reduce from 180 degree to 0
degree and become fix. As shown in fig 4.5, a simple instrumentation OP AMP circuit using U1,
U2, U3 is employed for this purpose. Output of instrumentation op amp is given by
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(
)
Generally we fix and vary according to LDR resistance variation. For finding the
appropriate timing to vary firing angle, we conduct the series of test. Normal Street light On time
is noted. And conduct a test to find the resistance of LDR at evening. From the experiment we
found that LDR resistance in noon is merely Ω. During evening it resistance increase from
few kΩ to kΩ in 5 min and then sharp changing is observed. For the LDR value in between
kΩ to kΩ, the output voltage is varying from - to . . For LDR alue above kΩ,
firing is occurring at 0 degree.
Fig 4.5 Automatic Variable D.C Voltage generator using LDR
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Circuit Implementation
Various portion of circuit is tested on MultiSim-10 before implementing it on breadboard. As per
the block diagram shown in fig 4.6, circuit is implemented in two step. Let us discuss both part
one by one.
Fig 4.6 Block diagram of implemented circuit
4.5 Automatic ON/OFF Circuit
The detail circuits diagram for the control of street light is shown in figure 4.7. The circuit
depends on a light sensitive device called LDR (light dependent resistor). The resistance of the
LDR depends on the amount of light falling on it. The simple circuit just which give a fix voltage
during evening when LDR resistance increase above 5kΩ can be used to switch transistor ON
and cause relay operate and street light start glowing. But this type of general circuit cause
frequent operation of relay during transient period. Even it damages the bulb or relay itself. For
avoiding this situation little bit complex OP AMP based circuit is used.
A set of LDR resistance reading is taken during evening and morning time. Data help us to find
the suitable operating point of this circuit. LDR resistance of 5kΩ is chosen as operating point of
relay. As shown in fig 4.7, R3, R9 and LDR formed on arm of bridge and R1 and POT formed
another arm. For the 5 kΩ resistance of LDR, voltage at port is .7 . Now by varying the
POT resistance, we set the voltage at port 2 is nearly equal to 4.74V. Terminal 1 and 2 is
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connected to the + and – input terminal of OP AMP. As open loop gain of OP amp is 10000, for
slightly variation of input voltage, the output is either 12 V or -12 V i.e for LDR resistance of
5. kΩ, the output is . During daytime LDR resistance is always less than 5 kΩ, so output is
-12 V. this cause voltage at 3 is - . and transistor remain off. Let‘s the evening or dark
condition, in this cause LDR resistance is greater than 5 kΩ and output at OP amp is 12V and
11.3 V at terminal 3. This is able to drive transistor and operate relay and cause relay coil turn
ON.
Fig 4.7 Relay operation circuit diagram
Table 1: LDR Resistance variation graph (on 18.03.2012)
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S.No Date Turn ON Time
1. 20.03.2012 6:38 PM
2. 21.03.2012 6:38 PM
3. 23.03.2012 6:40 PM
4. 24.03.2012 6:43 PM
Table 2: Turn ON Time of circuit
Fig 4.8 Experimental setup and circuit on PCB
4.6 TRIAC FIRING CIRCUIT
For intensity based control of street light, TRIAC is used whose firing angle change according to
the intensity. Circuit is design so that firing angle change from 130 to 0 degree for LDR
resistance change from 5 kΩ to kΩ. Fig .5 shows the Instrumentation OP amp circuit, which
generate Vref (according to light intensity) for changing firing angle automatically.
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Firing circuit is design using Integrator, comparator and logic Gate. As in fig 4.9 , the two input
reference Vao and Vbo is taken from supply for synchronizing the circuit. Vbo is a 180 degree
phase shift from Vao. At 1 & 2, there is wave of 90 degree shift of Vao and Vbo respectively.
Vref is used to generate the specific signal at 6 & 8, which decide the firing angle. The signal at
6 & 8 is conditioned to generate firing pulse at 9 & 10 respectively for positive and negative
cycle. The signal at 11 is used as firing pulse. Optocoupler is used as isolator between power and
firing circuit.
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Fig 4.10 Optocoupler interfacing circuit
Fig 4.11 Waveform at different points in the circuit of Fig4.9
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Fig. 4.12, Firing circuit implemented on Breadboard and PCB
Fig 4.13, Firing angle Pulse observe on CRO for different LDR resistance
4.7 Change in firing angle:
Firing angle variation is observed by varying the LDR resistance. By plotting a graph between Vref
voltage apply to firing circuit and firing angle, we found that firing angle is increase with increase in LDR
resistance. So, using this graph, it is found that circuit is suitable for controlling the power of circuit
during transient period and also save energy. The ultimate aim of saving energy and automatic control
of street light is achieved.
Output voltage of Load is given by
√ √
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Fig. 4.14 Graph for variation in firing angle with variation of Automatic Vref voltage
Fig. 4.15 graph to show Load power consumed for different firing angle for 200W lamp
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CHAPTER 5 CONCLUSION
5.1 Summary of the work reported in the project
This project deals with the design and development of suitable control circuit, for street light
using LDR.
First, a simple circuit using comparator is design to operate the relay switch, which turns
ON/OFF the street light. The circuit has been implemented on the breadboard by selecting
suitable value of resistance in bridge. The circuit is tested to find the reliability of circuit. Firing
circuit is designed using the cosine technique. The firing angle is varying as the Vref voltage is
change and the corresponding waveform is check using CRO. By controlling the firing angle
through the LDR sensor, the power output applied to a load through Triac is controlled
automatically by controlling firing angle.
5.2 Scope of future work
The work outlined in this project leads itself to the following scope of future work through
various sensor has the potential for automatic control of AC devices like fan, load, furnaces.
1. The present work control the conventional AC circuit, but now a day LED, solar based
low power street light is used. For that type of lightning load necessary to design the DC
based Automatic controller. This possible by modifying the present circuit by using
PWM technique.
2. It is used to control the humidity of fertilizer godown. We simply connect the humidity
sensor circuit to give the Vref voltage which decide the speed of blower motor and hence
regulate the blower.
3. For maintain the temperature of furnace.
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APPENDIX
Single Supply Quad Operational Amplifiers (LM324)
The LM324 series are low-cost, quad operational amplifiers with true differential inputs.they have
different distinct advantages over standard operational amplifier types in single supply applications.
The quad amplifier can operate at supply voltage as low as 3.0 V or as high as 32V. the common
mode input range includes the negative supply, therby eliminating the necessity for external biasing
components in many applications. The output voltage range also includes the negative power
supply voltage.
Features
1. Short circuit protected outputs
2. True differential Inputs stage
3. Single Supply Operation: 3.0 V to 32 V
4. Low Input Bias Currents: 100 nA maximum (LM324A)
5. Four OP- Amp available
6. Industry Standard Pin outs
7. Pb-Free Packages are available
Fig A.1 Pin diagram of LM324
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60
QUAD two-input OR gate (SN74LS32)
A Logic OR Gate or Inclusive-OR gate is a type of digital logic gate that has an output which is
normally at logic level "0" and only goes "HIGH" to a logic level "1" when ANY of its inputs are
at logic level "1". The output of a Logic OR Gate only returns "LOW" again when ALL of its
inputs are at a logic level "0". The logic or Boolean expression given for a logic OR gate is that
for Logical Addition which is denoted by a plus sign, (+) giving us the Boolean expression
of: A+B = Q.
A simple 2-input logic OR gate can be constructed using RTL Resistor-transistor switches
connected together as shown below with the inputs connected directly to the transistor bases.
Either transistor must be saturated "ON" for an output at Q.
Fig. A.2
Logic OR Gates are available using digital circuits to produce the desired logical function and is
given a symbol whose shape represents the logical operation of the OR gate.
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61
Fig A.3 Pin diagram of 74LS32
QUAD two-input AND gate (SN74LS08)
A Logic AND Gate is a type of digital logic gate that has an output which is normally at logic
level "0" and only goes "HIGH" to a logic level "1" when all of its inputs are at logic level "1".
The output of a Logic AND Gate only returns "LOW" again when any of its inputs are at a logic
level "0". The logic or Boolean expression given for a logic AND gate is that for Logical
Multiplication which is denoted by a single dot or full stop symbol, (.) giving us the Boolean
expression of: A.B = Q.
A simple 2-input logic AND gate can be constructed using RTL Resistor-transistor switches
connected together as shown below with the inputs connected directly to the transistor bases.
Both transistors must be saturated "ON" for an output at Q.
Fig. A.4 AND gate circuit
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62
Logic AND Gates are available using digital circuits to produce the desired logical function and
is given a symbol whose shape represents the logical operation of the AND gate.
TRIAC BT134
BT134 in a plastic envelope, intended use in application requiring high bidirectional transient
and have a blocking voltage capability and high thermal cycling performance. Typical
applications include motor control, industrial and domestic lighting, heating and static switching.
The conducting metal surface is provided for heat sink.
Repetitive Peak off state voltage……………….
RMS on state current…………………………..
Non – Repetitive Peak on- state current………. 5
Fig A.5 Pin Diagram of TRIAC BT 1
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63
REFRENCES
1. Tirtharaj Sen, Pijush Kanti Bhattacharjee, Member, I SIT, Manjima Bhattacharya,
―Design and Implementation of Firing ircuit for SinglePhase onverter‖, International
Journal of omputer and Electrical Engineering, ol. , No. , June
2. Wang ongqing, Hao huncheng, Zhang Suoliang,‖Design of Solar LED Street Lamp
utomatic ontrol ircuit‖, 9 International onference on Energy and Environment
Technology
3. R.W. Wall, Senior Member, IEEE, ‖Simple Methods for Detecting Zero rossing‖,
Proceedings of The 9th nnual onference of the IEEE Industrial Electronics Society
Paper # 9
4. Hengyu Wu, Minli Tang, Guo Huang,‖ Design of Multi-functional Street Light Control
System Based on AT89S52 Single-chip Microcomputer‖, nd International
Conference on Industrial Mechatronics and Automation.
5. Muhammad H. Rashid,‖Power Electronics‖, Prentice Hall of India Publishers Ltd, 9.
6. Paul B. Zbar and Albert P. Malvino, Basic Electronics: A Text – Lab Manual, 5th
edition,
Tata McGraw-Hill Publisher, 5Ω